PROJECT SUMMARY State-of-the art neural recording technologies for in vivo applications can record simultaneously from a few hundred microelectrode recording sites. These recording sites are passive electrodes wired to read-out circuitry outside the brain. The number of wires entering the brain is equal to number of recording sites. This one-to-one relationship between recording sites and access wires is a major obstacle to obtaining high-density recordings from large areas of the brain, preventing technology scaling to many thousands of electrodes. We propose to break the conventional N-wire, N-electrode array architecture using graphene bio-FET sensors to enable frequency-based multiplexing and shared sensor wires. Specifically, the goal of this project is to demonstrate a neural recording platform that has N recording sites accessed by 2?? wires. Such a technology would enable recording from 22,500 recording sites with only 300 wires entering the brain. A key component of our proposed architecture is active graphene electrodes that allow signal mixing at the recording site, and a frequency modulation scheme that allows sharing each interface wire among many active electrodes. The proposed project includes both design and nanofabrication of the flexible sensor array, as well as development and implementation of a custom integrated circuit architecture for the multiplex recording interface. By fabrication of atomically thin sensors on flexible substrates, we will provide dense, conformal neural sensor arrays for surface recordings. We aim to develop a scalable platform that can simultaneously achieve high signal count, high spatial resolution, and sufficient temporal precision to infer functional interactions between neurons.